Hermetic feedthrough for an implantable device

ABSTRACT

The present invention provides an implantable substrate sensor comprising electronic circuitry formed within, or on, a substrate. A protective coating then covers the substrate, forming a hermetically sealed package having the circuitry under the coating. The circuitry has electrically conductive pads for communicating and/or providing power to the circuitry. Electrical pathways provide hermetic electrical connection to the conductive pads for external connection to the sealed circuitry. In a first embodiment, the pathway is a via that is made from a biocompatible material that is made hermetic by either increasing its thickness or by ion beam deposition. Alternatively, the pathways are formed from metal traces, surrounded by a biocompatible insulation material, essentially parallel to the surface of the substrate that are connected to the conductive pads by first vias and have second ends externally accessible to the sealed package to provide external electrical connection to the hermetically sealed circuitry within.

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/100,310 filed Jun. 19, 1998, now allowed, whichin turn is a continuation-in-part of U.S. patent application Ser. No.08/928,867 filed Sep. 12, 1997, now U.S. Pat. No. 5,999,848.

FIELD OF THE INVENTION

[0002] The present invention is generally directed to an implantablemedical device, e.g., an implantable sensor, and in particular isrelated to techniques for providing hermetic connections to such adevice.

BACKGROUND OF THE INVENTION

[0003] The present invention relates to semiconductor substrates, andmore particularly to a semiconductor substrate fabricated to includehermetically-sealed electronic circuitry as well asnon-hermetically-sealed electrodes thereon so as to form an implantablesensor or other implantable electronic device.

[0004] In U.S. Pat. No. 5,660,163 (hereafter the '163 patent), there isdisclosed an implantable glucose sensor which is fabricated on a ceramicsubstrate. Working electrodes and other elements associated with thesensor are exposed to a conductive fluid contained within a reservoir orinner sheath that covers the substrate. An outer sheath is also placedover the sensor, with a window formed over one of the workingelectrodes. A selected enzyme, such as glucose oxidate (GO), is placedwithin the window. As disclosed in the '163 patent, five wires orconductors are attached to the electrodes and connected to electroniccircuitry, e.g., a circuit such as is shown in FIG. 3 of the '163patent. U.S. Pat. No. 5,660,163 is incorporated herein by reference inits entirety.

[0005] Additional features, aspects and improvements of a glucose sensorof the type disclosed in the '163 patent are further disclosed in U.S.patent application Ser. Nos. 08/953,817, filed Oct. 20, 1997, now U.S.Pat. No. 6,081,736; 08/954,166, filed Oct. 20, 1997, now U.S. Pat. No.6,119,028; and 08/928,867, filed Sep. 12, 1997, now U.S. Pat. No.5,999,848; all of which are assigned to the same assignee as the presentapplication and each of which is incorporated herein by reference in itsentirety.

[0006] As disclosed in the referenced patents, an improved implantablesensor may be fabricated by placing the electrodes on one side of thesubstrate and by also placing an integrated circuit (IC) chip on theother side of the substrate, along with other needed electroniccomponents, e.g., a capacitor(s), thereby forming a hybrid electroniccircuit on the side of the substrate opposite the electrodes that isused to control or drive the sensor. The sensor senses the electricalcurrent flowing to the electrodes, from which current the amount ofoxygen near the electrodes can be determined, from which oxygen leveldetermination, the amount of glucose to which the sensor is exposed canalso be determined. Additionally, the sensor sends and receivesinformation, data, and/or power from an external location over atwo-conductor transmission line. The IC chip and other electroniccomponents are hermetically sealed under a metal cover, the edges ofwhich are hermetically bonded to the substrate. Electrical connection isestablished with the IC chip and other sealed components throughstair-step vias or passageways that traverse through the substrate.Several of these types of sensors may be daisy-chained together, usingjust two conductors, as required. The outer sheath encircles the entiresubstrate, both the electronic circuit side with its metal cover, andthe sensor electrode side, with its electrodes, saline solutionreservoir and enzyme-filled window.

[0007] Disadvantageously, the sensor described in the referenced patentsand patent applications is relatively thick. For many implantableapplications, a thinner sensor is needed that still provides hermeticelectrical connections to its internal circuitry. Hence, there remains aneed for yet a smaller sensor that performs all of the same functions asthe prior sensor, i.e., that provides working electrodes exposed to asaline, with a selected enzyme placed over one electrode, and withhermetically-sealed electronic circuitry controlling the sensor andcommunicating with other sensors and an external control unit. Thepresent invention advantageously addresses these and other needs.

SUMMARY OF THE INVENTION

[0008] The present invention provides an implantable substrate sensorwherein electronic circuitry associated with the sensor, i.e., the ICchip, is formed within, or on, a suitable substrate, e.g., a CMOSsubstrate. A protective coating then covers the substrate, effectivelyforming a hermetically sealed package having the circuitry under thecoating. In embodiments of the present invention, the circuitry has oneor more electrically conductive pads for communicating and/or providingpower to the circuitry. One or more electrical pathways provide hermeticelectrical connection to the conductive pads for external connection tothe sealed circuitry within the sealed package. Electrodes associatedwith the sensor may be selectively left uncovered by the protectivecoating, thereby allowing such electrodes to be exposed to body tissueand fluids when the sensor is implanted in living tissue.

[0009] In a first embodiment, the electrical pathway is a via that ismade from a biocompatible material, e.g., platinum, that is madehermetic by either increasing its thickness, e.g., to at least 5microns, or by ion beam deposition. Alternatively, the electricalpathways are formed from metal traces essentially parallel to thesurface of the substrate that are connected at their first ends by firstvias to conductive pads on the circuitry and with their second endsextending external to the sealed package, thus providing externalelectrical connection to the hermetically sealed circuitry. The metaltraces are surrounded by a biocompatible insulation material, e.g.,alumina, zirconia, or alloys of alumina and zirconia. Due to thiscombination of vias and metal traces surrounded by insulation material,the resulting electrical connection is hermetic.

[0010] In accordance with one aspect of the invention, a pair of thinsubstrate sensors made in accordance with the present invention, eachhaving electronic circuitry formed on one side of the substrate may beplaced back-to-back with the interconnecting and/or sensing electrodesfacing outward. Such a back-to-back pair of substrate sensorsadvantageously allows the sensor electrodes to be positioned on theoutside surfaces of the sensor pair substrates.

[0011] A hermetically sealed package suitable for implantation in livingtissue comprises (1) a semiconductor substrate having a plurality ofsurfaces and having an integrated circuit formed on at least one of saidsurfaces, the integrated circuit having one or more electricallyconductive pads for communicating and/or providing power to theintegrated circuit, (2) one or more electrical pathways for providingelectrical connection to the one or more electrically conductive pads,the pathways having first ends coupled to the one or more pads andsecond ends exposed for external electrical connection from the sealedpackage, and (3) an insulating material for encapsulating the integratedcircuit and the semiconductor substrate surfaces except for selectedportions of the seconds ends of the electrical pathways.

[0012] The novel features of the invention are set forth withparticularity in the appended claims. The invention will be bestunderstood from the following description when read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION

[0013] The above and other aspects, features and advantages of thepresent invention will be more apparent from the following moreparticular description thereof, presented in conjunction with thefollowing drawings.

[0014]FIG. 1 is a block diagram that illustrates multiplesensors/stimulators connected together using a two-conductor bus, whichtwo-conductor bus may be connected to a controller.

[0015]FIG. 2 schematically illustrates a preferred manner of how asensor/stimulator may be connected with a controller and othersensors/stimulators in a serial or daisy-chain fashion.

[0016]FIG. 3A shows a perspective, partially exploded, view of asensor/stimulator of the type disclosed in the referenced patentapplication as used in the daisy chain of FIG. 2.

[0017]FIG. 3B illustrates a sectional side view of the sensor/stimulatorof FIG. 3A.

[0018]FIG. 3C illustrates a sectional top view of the sensor/stimulatorof FIG. 3A.

[0019]FIG. 3D illustrates a sectional end view of the sensor/stimulatorof FIG. 3A.

[0020]FIG. 4 depicts an implantable lead that includes a plurality ofthe sensor/stimulators of FIGS. 3A-3D.

[0021]FIGS. 5A and 5B respectively shows perspective and cross sectionalviews of a preferred sensor substrate made in accordance with thepresent invention, which provides a hermetic electrical connection to asemiconductor formed on the substrate by enhancing the hermeticity ofthe electrically conductive via.

[0022]FIGS. 6A and 6B respectively shows a perspective and a crosssectional view of an alternative embodiment of a preferred sensorsubstrate made in accordance with the present invention, which providesa hermetic connection to a semiconductor formed on substrate by forminga combination of via and metallic pathways surrounded by an insulatingmaterial.

[0023]FIG. 7 shows a partial cross section of a next alternativeembodiment of a technique for providing a hermetic electrical connectionto the semiconductor formed on the substrate.

[0024]FIG. 8 shows one method that may be used to deposit a protectivecoating or layer over the sensor substrate.

[0025]FIG. 9 illustrates a sensor assembly formed by placing two sensorsubstrates back-to-back so that the electrodes of both sensor substratesface outwardly from the assembly.

[0026]FIG. 10 depicts use of the sensor assembly of FIG. 9 within asheath and membrane to form an electrochemical sensor assembly.

[0027] Corresponding reference characters indicate correspondingcomponents throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The following description is of the best mode presentlycontemplated for carrying out the invention. This description is not tobe taken in a limiting sense, but is made merely for the purpose ofdescribing the general principles of the invention. The scope of theinvention should be determined with reference to the claims.

[0029] The following description of is of the best mode presentlycontemplated for carrying out the invention. This is made merely for thepurpose of describing the general principles of the invention. The scopeof the invention should be determined with reference to the claims.

[0030] At the outset, it is to be noted that implantable sensors aregenerally used to sense some type of physiological parameter orcondition or other event that occurs within, or is sensible from alocation within, living tissue of a patient. To that end, such sensorsemploy one or more electrodes, or similar transducers, that convert asensed parameter to an electrical or other detectable signal. Ofttimes,a sensor simply senses an electro-potential signal, such as that whichtypically accompanies depolarization of muscle tissue, or other naturalelectrical signals associated with the patient's body. In such aninstance, all the sensor need employ is some type of electrode that isin contact with the monitored tissue and appropriate electroniccircuitry for receiving, amplifying and/or storing any signal that issensed. Also, it is common to employ the electrode of such sensor as astimulator as well, through which an electrical current pulse may beapplied to tissue in contact with the electrode. Thus, it is common torefer to a sensor electrode, which also may be used as a stimuluselectrode, as a sensor/stimulator. Further, the sensor may be used as anelectrochemical sensor, or enzyme electrode sensor, e.g., of the typedisclosed in the '163 patent or the other referenced patents. For suchan electrochemical sensor, a suitable enzyme or other chemical is placedin close proximity to the electrodes so that the desired chemicalinteractions may take place.

[0031] Whatever the type of implantable sensor employed, a commonelement(s) in all such sensors is the electrode and the electroniccircuitry used to monitor and/or control the electrode(s). It is to beunderstood, however, that other sensor elements, e.g., an enzyme, may beused in conjunction with the electrode and associated electroniccircuitry.

[0032] To better understand and appreciate the advantages offered by thepresent invention, it will first be helpful to briefly review apreferred application and manner of making an implantable sensor of thetype disclosed in the referenced patent and patent applications. To thatend, reference is made to FIG. 1, where there is shown a block diagramthat illustrates multiple sensor/stimulators 12 a, 12 b, . . . 12 n,connected together, as well as to a controller (not shown) using justtwo common conductors 14 and 16. The two conductors 14 and 16 provide acommon signal and return for data signals and power signals that aresent from the controller to the sensor/stimulators 12 a, 12 b, . . . 12n, as well as a common signal and return path for data signalstransmitted from the sensor/stimulators 12 a, 12 b, 12 n, to thecontroller.

[0033]FIG. 2 schematically illustrates how an implantable device, e.g.,a sensor/stimulator 18 a, may be connected with a remote controller 20and other implantable sensor/stimulators 18 b, . . . 18 n, in a serialor daisy-chain fashion. As seen in FIG. 2, the sensor/stimulator 18 a isconnected to the controller 20 by two conductors 14′ and 16′ which areattached to a first pair of pads or terminals 13 and 15 along a proximalside (i.e., the side closest to the controller 20) of thesensor/stimulator 18 a. Another pair of pads or terminals 17 and 19 arelocated along a distal side (i.e., the side farthest from the controller20) of the sensor/stimulator 18 a. As will become evident from thedescription that follows, the distal pad 17 is electrically connected tothe proximal pad 13 through the circuitry 21 located on thesensor/stimulator 18 a. Similarly, the distal pad 19 is electricallyconnected to the proximal pad 15 through the circuitry 21 includedwithin the sensor/stimulator 18 a. Two additional conductors 14″ and 16″are then used to connect the distal pads 17 and 19 of the device 18 a tocorresponding proximal pads 13′ and 15′ of the next sensor/stimulator 18b connected in the daisy chain. In this manner, as many devices asdesired may be serially connected to the controller 20 using just twoconductors.

[0034] It is noted that FIG. 1 is functionally electrically equivalentto FIG. 2. FIG. 2 simply employs proximal and distal pairs of pads orterminals to facilitate the connection of additional devices to thechain by extending two conductors from the distal pads 17 and 19 of amore proximal device in the chain to the proximal pads 13′ and 15′ of anew device to be added to the chain. However, where the particularapplication allows connections to be made to, or branched off of, thetwo main conductors 14 and 16, then the configuration of FIG. 1 may beused just as well as the configuration of FIG. 2.

[0035] There exist many different applications for the daisy-chainablesensor/stimulators 12 or 18 of the system illustrated in FIGS. 1 or 2.Generally, where the sensor/stimulators 12 or 18 are implanted, they aredesigned to sense one or more body parameters or substances found inbody tissue or fluids, e.g., glucose level, blood pH, O₂, temperature,or the like. Such measurements can provide valuable informationregarding the condition and status of the patient. As such, it isofttimes desirable to make more than one measurement within the samegeneral body tissue area so as to be able to compute an average or meanof the measurements thus made or otherwise obtain a consensus fromseveral different readings, thereby better assuring the accuracy andreliability of the data thus gathered.

[0036] Other times, it may be desirable to obtain various measurementsof a given substance at physically related, but different, bodylocations. For example, for some applications, e.g., a closed-loopinsulin infusion system, it could be advantageous to obtain a glucosereading within the blood stream and another glucose reading within theblood stream and another glucose reading within the body tissue adjacentthe blood stream. This is because the time constant associated with howreadily one glucose reading changes compared with the other may bedifferent (and, in fact, is usually different), and being able to obtainor monitor such difference would provide valuable information regardingthe regulation of the insulin infusion.

[0037] Turning next to FIGS. 3A, 3B, 3C and 3D, there are shown,respectively, a perspective exploded view (FIG. 3A), a side view (FIG.3B), a top view (FIG. 3C), and an end view (FIG. 3D), of a typicalimplantable sensor device 30 of the type disclosed in the referencedpatents. As seen best in FIG. 3A, the sensor device 30 typicallyincludes a carrier or substrate 36 on which an integrated circuit (IC)38 and other components, such as a capacitor 40, are mounted in hybridfashion.

[0038] Whereas the carrier or substrate 36 shown in FIG. 3A serves as afoundation or base on which hybrid electronic circuitry is formed, thepresent invention relates to an embodiment where the carrier orsubstrate 36 actually comprises the substrate in which the IC 38 isformed.

[0039] For the embodiment shown in FIGS. 3A-3D, all of the components ofthe hybrid circuit are hermetically sealed within a cavity formed by alid or cover 42 which is bonded to the substrate 36. As will be evidentfrom the description that follows, a significant advantage of thepresent invention is that this lid or cover 42 is not required in theembodiment of the invention disclosed herein.

[0040] Returning to FIGS. 3A-3D, proximal pads or terminals 13 and 15,as well as distal pads or terminals 17 and 19, remain outside of thehermetically sealed part of the hybrid circuit created by the cover 42.These proximal and distal pads, however, are electrically connected tothe circuitry within the hermetically sealed part through suitablefeedthrough connections. One preferred manner of making such feedthroughconnection is to use a feedthrough connection that passes through thecarrier or substrate in the stair-step manner (including both verticaland horizontal segments) is disclosed in U.S. Pat. No. 5,750,926, which'926 patent is incorporated herein by reference.

[0041] Still with reference to FIGS. 3A-3D, on the side of the carrieror substrate opposite the hybrid electrical circuitry, a suitableelectrochemical sensor 44, or other desired type of sensor orstimulator, may be formed or located. A type of electrochemical sensorthat may be used, for example, is the enzyme electrode sensor describedin U.S. Pat. No. 5,497,772, incorporated herein by reference, and inparticular, in FIGS. 2A, 2B, 2C, 3, 4A and 4B of that patent. However,it is to be emphasized that the precise nature of the sensor 44, orother implantable element used within the sensor device 30, is notcritical to the present invention. All that matters is that the sensoror other element be implantable, and that it provide a desired function,e.g., sense a certain type of parameter or substance, or generate acertain type of signal, in response to an appropriate control signal orsignals.

[0042] Whatever type of control signal(s) or output signal(s) is/aregenerated by the sensor 44, or other element, such signal(s) may becommunicated from the hybrid circuit side of the carrier or substrate 36(which is the top side as the sensor device 30 is oriented in FIG. 3B orFIG. 3D, and which top side includes the hermetically sealed portion ofthe device) to the sensor side of the sensor device 30 (which is thebottom side as shown in FIG. 3B or FIG. 3D) by way of appropriatehermetically-sealed feedthroughs that pass step-wise from the hybrid(top) side of the sensor device 30 through the substrate or carrier,e.g., in the manner set forth in the above-referenced '926 patent, tothe sensor (bottom) side of the sensor device 30.

[0043] For example, where the sensor comprises a glucose sensor of thetype taught in U.S. Pat. No. 5,497,772, there may be five conductorsthat electrically interface with the main elements (electrodes) of thesensor, as seen best in FIG. 4A of the '772 patent. Where such a glucosesensor is employed, these five conductors thus interface with the hybridelectrical circuitry found on the top side of the carrier 36 usingappropriate feedthroughs that hermetically pass step-wise through thecarrier 36, i.e., that pass through the carrier using both verticalhorizontal segments, as taught in the '926 patent.

[0044] As mentioned above, the parent application is directed to adevice 30 that does not employ a carrier 36, per se, as shown in FIGS.3A, 3B, 3C, 3D and FIG. 4, wherein the control electronics arepositioned on one side (the top side) of the carrier 36, and the sensor,or other device being used with or controlled by the electronics, isplaced on the other side (the bottom side) of the carrier. Rather, theceramic or substrate on which the IC 38 is formed itself functions asthe carrier. In the parent application, this is accomplished using viasthat are formed in a substrate, or between various layers of anintegrated circuit as the integrated circuit (IC) is formed, function ashermetic feedthroughs, with selected layers and traces being coated asneeded with aluminum oxide, or other oxide coatings, in the mannertaught in the aforementioned '926 patent, and/or in U.S. patentapplication Ser. No. 08/994,515, filed Dec. 19, 1997, now U.S. Pat. No.6,043,437, incorporated herein by reference, in order to sealappropriate sections or portions of the IC so that the coated IC mayitself be implanted. Advantageously, when this is done, the sensor 44 orother implantable element used with or controlled by the IC may beformed on the back side (non-active side) of the IC substrate. Thus, acarrier, per se, is not needed because the IC substrate functions as thecarrier, and a lid or cover 42 is not needed.

[0045] An important advantage achieved with embodiments of the parentapplication is that the electrical circuitry formed within the substrateof the sensor allows the implantable device to be daisy chained withother similar implantable devices, while still allowing each individualdevice to be individually addressed, controlled and monitored from asingle controller 20. Such electrical circuitry, frequently referred tohereafter as the interface/control circuitry, is shown in FIGS. 3A, 3B,3C, 3D and 4 as being located on the “top” side of the carrier 36,predominantly underneath the cover 42 in a hermetically sealed portionof the sensor device 30. However, it is to be understood that inaccordance with the parent application, such interface/control isactually formed within the substrate, on an active side of suchsubstrate, and coated, as required, with a suitable coating, so as to behermetically sealed.

[0046] The configuration of FIG. 2 is especially well-suited whereseveral of the implantable devices are to be daisy-chained together toform a single lead 32, as shown in FIG. 4. As seen in FIG. 4, threesensor-type devices 30 a, 30 b, and 30 c of the type shown in FIGS.3A-3D are connected together via lead segments 46 a, 46 b, and 46 c.Each of the lead segments 46 a, 46 b, and 46 c, contain two conductors14, 16, and may be constructed in any suitable manner, e.g., with thetwo conductors being spirally wound within the lead segments, and withthe spiral windings being encased or covered within a sheath of siliconerubber, as in known in the lead art. (Note, that for purposes of FIG. 4each of the two conductors 14, 16 within the lead 32 is considered asone conductor, even though each is segmented within the individual leadsegments 46 a, 46 b and 46 c as it connects from the distal pad of onedevice to the proximal pad of another device.) A distal cap 34 coversthe distal pads of the end, or most-distal, sensor device 30 c of thelead 32.

[0047] Turning next to FIGS. 5A and 5B, a preferred substrate sensor 50made in accordance with the present invention is shown. Top andsectional side views of such substrate sensor 50 are shown in FIGS. 5Aand 5B, respectively. Advantageously, the substrate sensor 50 does notuse hybrid electronic circuitry nor require a hermetically-sealed lid orcover. Rather, the substrate sensor 50 includes a substrate 52, e.g., asilicone or ceramic substrate of the type commonly used in the formationof CMOS or other integrated circuits.

[0048] Electronic circuitry is formed as an integrated circuit 70 on anactive side of the substrate 52, within a region 54, in conventionalmanner, e.g., in accordance with conventional CMOS processingtechniques, and may extend down below the surface into the substrate 52.Hence, the circuit region 54 is shown in FIG. 5B as extending slightlyinto the body of the substrate 52. On the active surface of thesubstrate sensor 50, as seen in FIG. 5A, connection pads 13, 15, 17 an19 may be formed to allow the sensor substrate to be daisy-chained withother sensors, as taught in the previously referenced U.S. Pat. No.5,999,848.

[0049] The integrated circuit 70 (shown in the example of FIG. 5B asextending to the edge of the substrate 52) includes a plurality ofelectrically conductive pads 72 formed on its upper surface forcommunicating and/or providing power to the integrated circuit 70. Suchpads are formed from an electrically conductive material, e.g.,aluminum, or the like, in a conventional matter. The majority of thesubstrate 52 and the integrated circuit 70 formed within are coated witha biocompatible insulating material, e.g., alumina, zirconia, or analloy or alumina and zirconia, to hermetically encapsulate the packageforming the substrate sensor 50 using an encapsulation layer 56.Significantly, the present invention provides electrical connectionthrough the encapsulation layer 56 to the electrically conductive pads72 while maintaining the hermeticity of the package forming thesubstrate sensor 50. In a first embodiment, shown in FIG. 5B, a metallicvia (e.g., forming pads 15 and 19), preferably formed from platinum,passes through the encapsulation layer 56 in order to provide externalelectrical connection to the electrically conductive pads 72. The viasare preferably made hermetic in one of two techniques. In a firsttechnique, the layer of platinum forming the via is made thick enough,e.g., at least 5 microns, to overcome any non-uniformity of the platinumthat would tend to allow leakage. In a next technique, described furtherbelow, ion beam deposition can be used to form the platinum vias. Since,this process will form a more uniform layer of platinum, the thicknessof the platinum vias may be somewhat decreased while still beinghermetic.

[0050] Turning next to FIGS. 6A and 6B, an alternative technique isshown for providing external hermetic electrical connections through theencapsulation layer 56 to the electrically conductive pads, e.g., 72 aand 72 b, on the integrated circuit 70 (shown in the example of FIG. 6Bas extending to the edge of the substrate 52). In this technique, ametallic (e.g., aluminum, platinum) trace, e.g., trace 74, is formedessentially parallel to the surface of the substrate 52 and theintegrated circuit 70. A first end of the trace 74 is electricallycoupled to the electrically conductive pad, e.g., pad 72 b. A second end58 of the trace 74 is exposed through the encapsulation material 56 toform a pad 19 accessible at its outer surface. In the technique shown inFIG. 6B, hermeticity is achieved via the serpentine routing of theelectrical connection from the second end 58 of trace 74 to theconductive pad 72 b and by the relative length of the metal trace 74,e.g., the length of the metal trace is preferably at least 100 microns.Preferably, the metal trace is surrounded by thin, e.g., 1 micron,layers of encapsulation material, typically deposited as one or morefabrication steps.

[0051] Additional electrical connections, e.g., for forming sensingelectrodes E1 and E2 (see FIG. 6A) may also be formed on the samesurface as the power/communication pads 13, 15, 17, 19 and hermeticallyconnected to the integrated circuit 70 in a similar manner. Such sensingelectrodes may be used in combination with the integrated circuit 70 toform a sensor as described in the aforementioned patents.Advantageously, when desired, the previously described technique allowsall of the connections, circuitry and sensing electrodes to be formed onthe same surface of the substrate 52 and thus facilitates thefabrication of multiple, e.g., pairs of, sensors as described furtherbelow in the description of FIGS. 9 and 10.

[0052]FIG. 7 shows a partial cross section of a next alternativeembodiment of a technique for providing a hermetic electrical connectionto the semiconductor formed on the substrate. This embodiment is similarto that shown in reference to FIG. 6A except that additional layers ofinterconnected metallic electrically conductive traces, 74′, 74″surrounded by additional encapsulation layers 56′, 56″, 56′″ are used tofurther enhanced the hermeticity of the electrical connection (at somecost in increased thickness of the package).

[0053] Various techniques may be used to apply a coating ofencapsulation layer 56, e.g., alumina insulation, over the substrate 52.A preferred technique, for example, is to use an ion beam deposition(IBD) technique. IBD techniques are known in the art, as taught, e.g. inU.S. Pat. Nos. 4,474,827 or 5,508,368, incorporated herein by reference.

[0054] Using such IBD techniques, or similar techniques, the desiredalumina or other layer 56 may be deposited on all sides of the substrate52 as illustrated in FIG. 8. As seen in FIG. 8, the substrate 52 isplaced on a suitable working surface 401 that is rotatable at acontrolled speed. The working surface 401 with the substrate 52 thereon(once the circuitry and electrodes have been formed thereon) is rotatedwhile a beam 421 of ions exposes the rotating surface. Assuming thesubstrate 52 has six sides, five of the six sides are exposed to thebeam 421 as it rotates, thereby facilitating application of the desiredlayer of alumina onto the five exposed sides of the object. Aftersufficient exposure, the object is turned over, thereby exposing thepreviously unexposed side of the substrate to the beam, and the processis repeated. In this manner, four of the sides of the substrate 52 maybe double exposed but such double exposure simply results in a thickerencapsulation layer 56 of alumina on the double-exposed sides.

[0055] Other techniques, as are known in the art, may also be used toapply the alumina encapsulation layer 56 to the object.

[0056] The steps typically followed in applying an encapsulation layer56 of alumina to the substrate 52 include:

[0057] (a) Sputtering a layer of titanium of about 300 Å thick over anymetal conductor or other object that is to be coated with the alumina.

[0058] (b) If selective application of the alumina to the object is tobe made, spinning a photosensitive polyamide onto the substrate.

[0059] (c) Applying a mask that exposes those areas where alumina is notto be applied.

[0060] (d) Shining ultraviolet (UV) light through the mask to polymerizethe polyamide. Where the UV light illuminates the polyamide is wherealuminum oxide will not be deposited. Thus, the polymerizations of thepolyamide is, in effect, a negatively acting resist.

[0061] (e) Developing the photoresist by washing off the unpolymerizedpolyamide with xylene, or an equivalent substance. Once theunpolymerized polyamide has been washed off, the ceramic (or othercomponent) is ready for aluminum oxide deposition.

[0062] (f) If selective application of the alumina is not to be made,i.e., if alumina is to be applied everywhere, or after washing off theunpolymerized polyamide, depositing aluminum oxide to a prescribedthickness, e.g., between 4 and 10 microns, e.g., 6 microns, over thesubject using ion enhanced evaporation (or sputtering), IBD, or othersuitable application techniques.

[0063] (g) During application of the coating, rotate and/or repositionthe substrate as required in order to coat all sides of the substrate,e.g., as shown in FIG. 8, with a coating of sufficient thickness. Thisstep may require several iterations, e.g., incrementally depositing athin layer of alumina, checking the layer for the desired thickness orproperties, and repeating the repositioning, depositing, and checkingsteps as required until a desired thickness is achieved, or until thecoating exhibits desired insulative and/or hermeticity properties.

[0064] (h) Breaking or scribing the aluminum oxide that resides over thepolyamide, if present, with a diamond scribe, or laser, controller by acomputerized milling machine. This permits a pyrana solution, explainedbelow, to get under the oxide for subsequent lift off of the aluminumoxide.

[0065] (i) Lifting off the polyamide and unwanted aluminum oxide aftersoaking the substrate in pyrana solution (H₂SO₄×H₂O₂×2 heated to 60°C.). Soaking should occur for 30 to 60 minutes, depending on thethickness of the polyamide layer.

[0066] The above described coating method is substantially the same asthat disclosed in the referenced U.S. Pat. No. 6,043,437, previouslyincorporated herein by reference. It should be apparent to one ofordinary skill in the art that the aforementioned IBD techniques may beadapted to selectively deposit a layer of platinum or the like of abiocompatible electrically conductive metal to form the via andelectrodes used to provide an external electrical interconnection to thesemiconductor formed within. Advantageously, by using such an IBDtechnique, the platinum or the like metallic layer can be madesufficiently uniform to provide a hermetic connection.

[0067]FIG. 9 illustrates a sensor assembly 100 formed by placing twosensor substrates 50 back-to-back so that the electrodes of both sensorsubstrates face outward. The protective encapsulation layer 56 is notshown in FIG. 9, but it is presumed to be present.

[0068]FIG. 10 depicts the use of the sensor assembly 100 of FIG. 9within a sheath 102 and membrane 104 so as to form an electrochemicalsensor assembly 110. The sheath 102 surrounds the sensor assembly 100and forms a reservoir therein into which a suitable solution 108, e.g.,a saline solution, is held. The membrane 104 surrounds the sheath 102.Pockets 106 are formed in the membrane 104 over a selected workingelectrode. A suitable enzyme 107 is placed inside of the pockets.Windows 109 expose the enzyme 107 to the surrounding environment held inthe pockets 106.

[0069] Operation of the electrochemical sensor assembly 110 may besubstantially as described in the '163 patent and the other previouslyreferenced patents. However, in the aforedescribed structure of sensorassembly 110, the sensing windows 109 are located on both sides of theassembly, thereby providing a broader exposure coverage or “view” forthe operation of the sensor.

[0070] As described above, it is thus seen that the present inventionprovides and implantable sensor having electrodes and electroniccircuitry, where the electronic circuitry and electrodes are formed onor in the same substrate material, e.g., a semiconductor substrate ofthe same type used in the formation of complementary metal oxidesemiconductor (CMOS) integrated circuits.

[0071] It is a further seen that the invention provides and implantablesensor, including electrodes and electronic circuitry, that does notrequire a lid or cover for hermetically sealing hybrid electroniccircuitry on one side of a substrate; thereby allowing the sensor to besignificantly thinner than would otherwise be possible.

[0072] While the invention herein disclosed has been described by meansof specific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims. Forexample, it is generally desirable that the corners of the assembly berounded (see corner 62 in FIG. 6B) to further ensure hermeticity.Sandblasting and acid etching techniques can accomplish this rounding.Furthermore, while pads, e.g., 19, are generally positioned within ashallow cavity in the encapsulation layer 56, it may be desired to bondconductive beads or pads to assist external connection or tostagger/layer the surrounding encapsulation layer to minimize any stresson external connections to the pads, e.g., 19. Such variations areconsidered to be within the scope of the present invention. It istherefore to be understood that within the scope of the claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A hermetically sealed package suitable for implantation in living tissue, said package comprising: a semiconductor substrate having a plurality of surfaces and having an integrated circuit formed on at least one of said surfaces, said integrated circuit having one or more electrically conductive pads for communicating and/or providing power to said integrated circuit; one or more electrical pathways for providing electrical connection to said one or more electrically conductive pads, said pathways having first ends coupled to said one or more pads and second ends exposed for external electrical connection from said sealed package; and an insulating material for encapsulating said integrated circuit and said semiconductor substrate surfaces except for selected portions of said seconds ends of said electrical pathways.
 2. The hermetically sealed package of claim 1 wherein said electrical pathway comprises a biocompatible hermetic via.
 3. The hermetically sealed package of claim 2 wherein said hermetic via is comprised of platinum.
 4. The hermetically sealed package of claim 3 wherein said hermetic platinum via is formed by ion beam deposition.
 5. The hermetically sealed package of claim 3 wherein said platinum via is made hermetic by having the thickness of the platinum via being at least 5 microns.
 6. The hermetically sealed package of claim 1 wherein each of said electrical pathways comprises: a first electrically conductive via electrically coupled to one of said pads; a metal trace having first and second ends oriented essentially parallel to the surface of the semiconductor substrate and electrically coupled at said first end to said first via, wherein said second end is at least partially externally exposed; and wherein said electrical pathway is surrounded by a biocompatible insulation material.
 7. The hermetically sealed package of claim 6 wherein said biocompatible insulation material is selected from the group of alumina, zirconia, or an alloy of alumina and zirconia.
 8. The hermetically sealed package of claim 6 wherein said second via is biocompatible.
 9. The hermetically sealed package of claim 8 wherein said second via is platinum.
 10. The hermetically sealed package of claim 1 wherein at least one of said electrically conductive pathways is comprised of: a plurality of metal traces having first and second ends, including at least an innermost trace closest to said semiconductor substrate and an outermost trace furthest from said semiconductor substrate, each adjacent pair of metal traces separated by an insulating material sandwiched in-between so as to form a hermetic seal between said metal traces; at least one interconnection via surrounded by said insulating material for interconnecting said adjacent pairs of metal traces; at least one innermost via for interconnecting said innermost trace to at least one of said pads on said integrated circuit; an insulating material for encapsulating said plurality of metal traces, said integrated circuit and said semiconductor substrate, wherein the second end of at least one outermost metal trace is at least partially exposed through the encapsulating insulating material for external communication; and wherein said combination of metal traces, sandwiched insulating material, encapsulating material and vias provides a hermetic communication path to said integrated circuit from a location external to said implantable package.
 11. The hermetically sealed package of claim 1 wherein said integrated circuit is formed on a first surface of the semiconductor substrate and said electrical pathways from said integrated circuit extend outward from said first surface.
 12. The hermetically sealed package of claim 1 1 wherein said semiconductor substrate has a second surface on a side opposite of said first surface and said second side of said substrate and is formed without electrical pathways or an integrated circuit, thereby facilitating connection of said second sides of two of said packages.
 13. A method of forming an electrically conductive hermetic connection to a hermetically sealed integrated circuit, said method comprising the steps of: forming an integrated circuit on a face of a semiconductor substrate, said integrated circuit having one or more electrically conductive pads for communicating and/or providing power to said integrated circuit; forming one or more electrical pathways for providing electrical connection to said one or more electrically conductive pads; said pathways having first ends coupled to said one or more pads and second ends exposed for external electrical connection from said sealed integrated circuit; and encapsulating said semiconductor substrate and said integrated circuit except for selected portions of said second ends of said electrical pathways.
 14. The method of claim 13 wherein the step of forming one or more electrical pathways comprises the step of forming said electrical pathways from a biocompatible material.
 15. The method of claim 13 wherein the step of forming one or more electrical pathways comprises the step of forming said electrical pathways from platinum such that said electrical pathways are biocompatible.
 16. The method of claim 15 wherein the step of forming said electrical pathways from platinum comprising depositing said platinum using ion beam deposition.
 17. The method of claim 15 wherein the step of forming said electrical pathways from platinum comprising depositing a layer of platinum of at least 5 microns to cause said platinum vias to be hermetic.
 18. The method of claim 13 wherein the step of forming one or more electrical pathways comprises at least in part the steps of: forming a first electrically conductive via electrically coupled to one of said pads; forming a metal trace having first and second ends oriented essentially parallel to the surface of the semiconductor substrate and electrically coupled at said first end to said first via, wherein said second end of said metal trace is at least partially externally exposed; and surrounding said electrical pathway by a biocompatible insulation material.
 19. The method of claim 18 wherein the step of surrounding said electrical pathway comprises depositing alumina to surround said electrical pathway.
 20. The method of claim 18 wherein the step of forming a second electrically coupled via comprises forming said second via from a biocompatible material.
 21. The method of claim 18 wherein the step of forming a second electrically coupled via comprises forming said second via from platinum such that said second via is biocompatible.
 22. The method of claim 13 wherein the step of forming one or more electrical pathways comprises at least in part the steps of: forming a plurality of metal traces having first and second ends, including at least an innermost trace closest to said semiconductor substrate and an outermost trace furthest from said semiconductor substrate, each adjacent pair of metal traces separated by an insulating material sandwiched in-between so as to form a hermetic seal between said metal traces; forming at least one interconnection via surrounded by said insulating material for interconnecting said adjacent pairs of metal traces; forming at least one innermost via for interconnecting said innermost trace to at least one of said pads on said integrated circuit; depositing an insulating material for encapsulating said plurality of metal traces, said integrated circuit and said semiconductor substrate; enabling at least a portion of one said second end of an outermost metal trace to be partially externally exposed through the encapsulating insulating material for external communication; and wherein said combination of metal traces, sandwiched insulating material, encapsulating material and vias provides a hermetic communication path to said integrated circuit from a location external to said implantable package.
 23. The method of claim 13 additionally comprising the step of rounding at least one corner of said encapsulated integrated circuit.
 24. The method of claim 23 wherein said rounding step comprises sandblasting.
 25. The method of claim 23 wherein said rounding step comprises acid etching. 